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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef CountingAllocatorBase_h
+#define CountingAllocatorBase_h
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Atomics.h"
+#include "nsIMemoryReporter.h"
+
+namespace mozilla {
+
+// This CRTP class handles several details of wrapping allocators and should
+// be preferred to manually counting with MOZ_DEFINE_MALLOC_SIZE_OF_ON_ALLOC
+// and MOZ_DEFINE_MALLOC_SIZE_OF_ON_FREE. The typical use is in a memory
+// reporter for a particular third party library:
+//
+// class MyMemoryReporter : public CountingAllocatorBase<MyMemoryReporter>
+// {
+// ...
+// NS_IMETHOD
+// CollectReports(nsIHandleReportCallback* aHandleReport,
+// nsISupports* aData, bool aAnonymize) override
+// {
+// MOZ_COLLECT_REPORT(
+// "explicit/path/to/somewhere", KIND_HEAP, UNITS_BYTES,
+// MemoryAllocated(),
+// "A description of what we are reporting.");
+//
+// return NS_OK;
+// }
+// };
+//
+// ...somewhere later in the code...
+// SetThirdPartyMemoryFunctions(MyMemoryReporter::CountingAlloc,
+// MyMemoryReporter::CountingFree);
+template<typename T>
+class CountingAllocatorBase
+{
+public:
+ CountingAllocatorBase()
+ {
+#ifdef DEBUG
+ // There must be only one instance of this class, due to |sAmount| being
+ // static.
+ static bool hasRun = false;
+ MOZ_ASSERT(!hasRun);
+ hasRun = true;
+#endif
+ }
+
+ static size_t
+ MemoryAllocated()
+ {
+ return sAmount;
+ }
+
+ static void*
+ CountingMalloc(size_t size)
+ {
+ void* p = malloc(size);
+ sAmount += MallocSizeOfOnAlloc(p);
+ return p;
+ }
+
+ static void*
+ CountingCalloc(size_t nmemb, size_t size)
+ {
+ void* p = calloc(nmemb, size);
+ sAmount += MallocSizeOfOnAlloc(p);
+ return p;
+ }
+
+ static void*
+ CountingRealloc(void* p, size_t size)
+ {
+ size_t oldsize = MallocSizeOfOnFree(p);
+ void *pnew = realloc(p, size);
+ if (pnew) {
+ size_t newsize = MallocSizeOfOnAlloc(pnew);
+ sAmount += newsize - oldsize;
+ } else if (size == 0) {
+ // We asked for a 0-sized (re)allocation of some existing pointer
+ // and received NULL in return. 0-sized allocations are permitted
+ // to either return NULL or to allocate a unique object per call (!).
+ // For a malloc implementation that chooses the second strategy,
+ // that allocation may fail (unlikely, but possible).
+ //
+ // Given a NULL return value and an allocation size of 0, then, we
+ // don't know if that means the original pointer was freed or if
+ // the allocation of the unique object failed. If the original
+ // pointer was freed, then we have nothing to do here. If the
+ // allocation of the unique object failed, the original pointer is
+ // still valid and we ought to undo the decrement from above.
+ // However, we have no way of knowing how the underlying realloc
+ // implementation is behaving. Assuming that the original pointer
+ // was freed is the safest course of action. We do, however, need
+ // to note that we freed memory.
+ sAmount -= oldsize;
+ } else {
+ // realloc failed. The amount allocated hasn't changed.
+ }
+ return pnew;
+ }
+
+ // Some library code expects that realloc(x, 0) will free x, which is not
+ // the behavior of the version of jemalloc we're using, so this wrapped
+ // version of realloc is needed.
+ static void*
+ CountingFreeingRealloc(void* p, size_t size)
+ {
+ if (size == 0) {
+ CountingFree(p);
+ return nullptr;
+ }
+ return CountingRealloc(p, size);
+ }
+
+ static void
+ CountingFree(void* p)
+ {
+ sAmount -= MallocSizeOfOnFree(p);
+ free(p);
+ }
+
+private:
+ // |sAmount| can be (implicitly) accessed by multiple threads, so it
+ // must be thread-safe.
+ static Atomic<size_t> sAmount;
+
+ MOZ_DEFINE_MALLOC_SIZE_OF_ON_ALLOC(MallocSizeOfOnAlloc)
+ MOZ_DEFINE_MALLOC_SIZE_OF_ON_FREE(MallocSizeOfOnFree)
+};
+
+} // namespace mozilla
+
+#endif // CountingAllocatorBase_h